The present application claims priority to Japanese Application(s) No(s). P2001-006384 filed Jan. 15, 2001, which application(s) is/are incorporated herein by reference to the extent permitted by law.
The present invention relates to a semiconductor device including a plurality of semiconductor elements stacked to each other and a structure of the semiconductor device, and particularly to a technique of thinning a semiconductor device by stacking a plurality of semiconductor elements to each other at a higher density.
If one semiconductor element is mounted on a wiring board, then an area of the wiring board is occupied with the semiconductor device, and thereby another semiconductor element is no longer mounted on the wiring board. On the other hand, in recent years, electronic devices such as video cameras, CDs, and portable telephones have been required to be further reduced in size and further enhanced in performance. To meet such a requirement, there has been proposed a semiconductor device, in which a semiconductor element mounting area becomes twice that of a prior art semiconductor device although the semiconductor device uses the same wiring board as that used for the related art semiconductor device.
The above-described related art semiconductor device, which is designated by reference numeral 1 in FIG. 4, includes two semiconductor elements 3 and 5, wherein a surface (back surface) 9 opposed to an electric connection surface 7 of the semiconductor element 3 is superimposed to a surface (back surface) 13 opposed to an electric connection surface 11 of the other semiconductor element 5 and is bonded thereto with adhesive 15, and the electric connection surface 11 of the upper semiconductor element 5 is electrically connected to segments 21 of wiring on a wiring board 19 by means of bonding wires 17 while the electric connection surface 7 of the lower semiconductor element 3 is electrically connected to segments 25 of the wiring on the wiring board 19 by means of bumps 23.
With this configuration, a mounting density of the semiconductor device becomes twice that of a conventional semiconductor device in which a mounting area is occupied with one semiconductor element. Accordingly, it is possible to miniaturize an electronic device using the semiconductor device.
The above-described related art semiconductor device, however, has a problem that since the back surfaces of the two semiconductor elements are fixed to each other, the upper semiconductor element has the electric connection surface on the upper side, and accordingly, any other semiconductor device is no longer stacked on the upper semiconductor element. That is to say, the related art semiconductor device cannot be configured to have a stacked structure of two or more layers. The related art semiconductor device has another problem that since the upper surface of the upper semiconductor element is taken as the electric connection surface and the bonding wires are connected to the electric connection surface, wire loops 17a (see FIG. 4) of the bonding wires project upwardly from the upper surface of the upper semiconductor element, so that the total height of the semiconductor device becomes correspondingly higher. This causes an obstacle to thinning the whole semiconductor device.
An object of the present invention is to provide a semiconductor device having a stacked structure of a plurality of semiconductor elements, which is capable of increasing a mounting density thereof and reducing a thickness thereof, thereby miniaturizing an electronic device using the semiconductor device, and to provide a structure of the semiconductor device.
To achieve the above object, according to a first aspect of the present invention, there is provided a semiconductor device bonded to a wiring board, including a semiconductor element; a bump for flip chip bonding formed on a surface of the semiconductor element; and a wiring pattern for connecting to a bump and a bonding wire of another semiconductor element, formed on the other surface of the semiconductor element.
With this configuration, since the wiring pattern to which the bump and the bonding wire for another semiconductor element are connected is formed on the other surface of the semiconductor element, another semiconductor element can be bonded to the other surface of the semiconductor element in a flip-chip bonding manner, and the bonding wires can be connected to the bumps of another semiconductor element via the wiring pattern. A semiconductor device of a type in which a back surface of a semiconductor element is used as a surface to which another semiconductor element is fixed has been known; however, in this semiconductor device, the back surface of the semiconductor element is used only as the means for fixing another semiconductor element. On the contrary, according to the present invention, the other surface, provided with the wiring pattern, of the semiconductor element can be used not only as the fixing means but also as a wiring surface similar to that of a usual wiring board. As a result, it is possible to realize high density mounting to a wiring board by making more effective use of the other surface of the semiconductor element.
According to a second aspect of the present invention, there is provided a semiconductor device structure including: a first semiconductor element bonded to a wiring board as a flip chip; a wiring pattern formed on a back surface of the first semiconductor element, and connected to a wire formed on the wiring board by means of a bonding wire; and a second semiconductor element bonded to the back surface of the first semiconductor element as a flip chip.
With this configuration, the first semiconductor element is bonded to the wiring board in a flip-chip bonding manner and the second semiconductor element is bonded to the back surface of the first semiconductor element in a flip-chip bonding manner, and the wiring pattern of the first semiconductor element is connected to the wiring board by means of the bonding wires. As a result, electrodes of the second semiconductor element can be led from the back surface of the first semiconductor element. According to the related art structure in which the back surface of the second semiconductor element is fixed to the back surface of the first semiconductor element, the bonding wires are connected to the front surface of the second semiconductor element (uppermost surface of the stacked structure), and thereby the bonding wires project from the uppermost surface of the stacked structure by an amount equivalent to a height of the wire loops, with a result that the total height of the semiconductor device becomes high. On the contrary, according to the present invention, since the bonding wires are led from the back surface of the first semiconductor element, the height of the wire loops is contained within a thickness of the second semiconductor element. As a result, the wire loops do not project from the uppermost surface of the stacked structure, to realize thinning of the semiconductor device including a plurality of semiconductor elements stacked to each other.
The above-described semiconductor device structure may further comprise a plurality of semiconductor elements having a wiring pattern formed on a back surface respectively, and multi-stacked on the back surface of the first semiconductor element as flip chips, wherein each the wiring pattern is connected to a wire formed on the wiring board by means of a bonding wire.
With this configuration, adjacent two of the semiconductor elements stacked in the vertical direction are bonded to each other in a flip-chip bonding manner, and the wiring pattern formed on the bask surface of each of the plurality of semiconductor elements is connected to segments of wiring formed on the wiring board by means of bonding wires. In the related art semiconductor device having the structure that the back surface of the second semiconductor element is fixed to the back surface of the first semiconductor element, the semiconductor device is of a stacked structure of two semiconductor elements. On the contrary, according to the present invention, two or more semiconductor elements can be stacked to each other, to realize a semiconductor device with a higher mounting density.
The above-described semiconductor device structure may be configured such that at least two of the wiring patterns, which are formed on the different semiconductor elements, are connected by means of a bonding wire.
With this configuration, since arbitrary segments of the wiring patterns formed on the back surfaces of different two of the semiconductor elements are connected to each other, those located on arbitrary layers of the semiconductor elements can be connected to each other. As a result, it is possible to increase the degree of freedom in design of wiring of a semiconductor device of a multi-layer structure, and hence to omit useless bonding wires and shorten the bonding wires and thereby simplify the wiring structure.